In conventional ultrasonic imaging, a focused beam of ultrasound energy is transmitted into body tissues to be examined and the returned echoes are detected and plotted to form an image. While ultrasound has been used extensively for diagnostic purposes, conventional ultrasound has been greatly limited by depth of scanning, speckle noise, poor lateral resolution, obscured tissues and other such problems.
Significant improvements have been made in the field of ultrasound imaging with the creation of multiple aperture imaging, examples of which are shown and described in Applicant's U.S. Pat. No. 8,007,439 issued Aug. 30, 2011 and titled Method and Apparatus to Produce Ultrasonic images Using Multiple Apertures, U.S. patent application Ser. No. 13/029,907, filed Feb. 18, 2010, titled “Point Source Transmission and Speed-Of-Sound Correction Using Multiple-Aperture Ultrasound. Imaging, and U.S. patent application Ser. No. 12/760,375, filed Apr. 4, 2010, titled “Universal Multiple Aperture Medical Ultrasound Probe,” all three of which are incorporated herein by reference. Multiple aperture imaging methods and systems allow for ultrasound signals to be both transmitted and received from separate apertures.
One problem with multiple aperture imaging is that it can be difficult to know the exact position of the elements of a large apparatus with multiple and separate physical points of contact (“footprints”) on the patient. It is desirable for each element position to be known to within 1/10 wavelength (for example, 0.03 mm at 3 MHz). In contrast, with conventional ultrasound probes, regardless of array vertical displacement or integration (e.g. 1.5D or 2D), there has never been a need to solve alignment and position issues between multiple arrays or multiple individual elements. The calibration methods and apparatuses described herein teach how to solve these problems for Universal Multiple Aperture ultrasound probes.